Identification of a novel proliferation-inducing determinant using lentiviral expression cloning

One of the major challenges in the post-genome era is the correlation between genes and function or phenotype. We have pioneered a strategy for screening of cDNA libraries, which is based on sequential combination of lentiviral and oncoretroviral expression systems and can be used to identify proliferation-modulating genes. Screening of a lentiviral expression library derived from adult human brain cDNA resulted in cloning of the potent proliferation-inducing determinant termed pi1 (proliferation inducer 1). Transduction experiments using GFP-expressing oncoretroviruses to target proliferation-competent cells suggested that overexpression of pi1 initiates proliferation of human umbilical vein endothelial cells (HUVECs). Growth induction of HUVECs as well as Swiss3T3 fibroblasts was confirmed by Brd-uridine incorporation assays, which correlated increased DNA synthesis with expression of pi1. The identified pi1 cDNA is 297 bp long and encodes a 10 kDa polypeptide. Since deregulation of proliferation control accounts for a number of today's untreatable human diseases such as neurodegenerative disorders and cancer, discovery of novel proliferation-modulating genes is essential for developing new strategies for gene therapy and tissue engineering.